In the related art, there is a known fiber-illumination type microscope in which a light source and a microscope body are connected by an optical fiber (for example, see Patent Literature 1). With illumination using an optical fiber, as with the microscope described in Patent Literature 1), the illumination intensity at a specimen surface may not be uniform, and patchy noise may be observed in the image due speckles caused by light interference between different transmission modes in a multimode fiber.
Thus, by employing a mode scrambler on the optical fiber, a mode scrambling effect due to refractive index changes in the optical fiber is used to give uniform radiation of the illumination light at the specimen surface (for example, see Patent Literature 2 and Patent Literature 3).
Known mode scramblers include, for example, those in which the optical fiber is curved or wound (for example, see Patent Literature 4), those in which external pressure is applied to the optical fiber to give a stress thereto (for example, see Patent Literature 5), those in which vibrations are applied to the optical fiber (for example, see Patent Literature 6, 7 and 8), and so forth. In addition, a technique in which an effect identical to mode scrambling is obtained by disposing a diffusion plate or the like in the optical path and moving the diffusion plate is also known (for example, see Non Patent Literature 1).